Human respiratory syncytial virus (RSV) is an enveloped RNA-containing virus of the paramyxovirus family of Order Mononegavirales (the nonsegmented negative strand RNA viruses). RSV is the most important viral agent of pediatric respiratory tract disease worldwide. Other members of the Order include measles, mumps, rabies and Ebola viruses. The RSV genome is a single negative strand of RNA of 15,222 nucleotides that encodes 10 major mRNAs and 11 proteins, as we have shown previously. The purpose of this project is to identify the functions of the viral proteins and to reconstruct events in the viral growth cycle under conditions where they can be more readily studied. Knowledge of the functions of the proteins is important for a basic understanding of this important human pathogen and for the design of live-attenuated recombinant vaccine viruses.We previously developed an experimental system for RSV based on the intracellular coexpression and assembly of viral RNA and protein components from recombinant plasmid vectors. This involves transfecting cultured cells with plasmids which individually encode a truncated version of negative-sense genomic or positive-sense antigenomic RNA (the latter being an intermediate in RNA replication) as well as whatever mix of RSV proteins is desired. In this way, various steps in the viral replication cycle can be reconstituted, such as genome replication, gene expression, gene regulation, packaging and infection. Because each component is expressed individually, each can be manipulated individually with regard to relative amount as well as by mutagenesis for structure-function studies. - virus, respiratory tract disease, infectious disease, pediatrics, vaccines, live- attenuated viral vaccine, recombinant DNA, proteins